Coded track circuit for railway traffic control



y 1942- H. A. THOMPSON comm) TRACK cmcuns FOR RAILWAY TRAFFIC CONTROL 2 Sheets-Shee t 1 Filed Sept. 27, 1941 n 9 9m d fi w 6 UJ b a, m m 7 5 1 P 0] Q WJUJ W P w W 0 M Q m m T W fi 6i 5/ 5 P U m g 1 QM 3 zw 7 J1 2 H R T h m k F-JIM- a 9 INVENTOR Patented May 5, 194-2 CQDED TRACK CIRCUIT FOR RAIL-WAY TRAFFIC CQNTROL Howard A Thompson, Edgewood, Pa, assignor to The Union Switch & Signal Company, Swis vale, Pa., a corporation of Pennsylvania Application September 27, 1%41, Serial No. 412,624

14 Claims.

My invention relates to track circuits for use in systems of railway trafiic control and it has special reference to the employment by such track circuits of operating energy that is periodically interrupted at one or more distinctive code rates.

Generally stated, the object of my invention is to lower the power requirements and improve the performance characteristics of track circuits of the coded class just named.

A more specific object is to render the relays of such track circuits highly immune to false operation by foreign current that may be p esent in the track rails.

Another object is to eliminate operating difficulties due to persistance of storage energy in the track ballastand rails following each pulse of coded energy that is applied thereto.

An additional object is to minimize the effect of code distortion on the operation of track cir- 1i cuits of the coded type herein considered.

A further object is to improve the shunting sensitivity of coded track circuits and to extend the length over which such circuits may be operated with a given level of applied energy.

A still further object is to provide improved facilities for impressing the coded energy upon the track rails and for imparting a highly effective character to the pulses of that energy.

A still additional object is to organize the improved facilities in such manner that the resulting track circuits are readily usable in signaling systems of the frequency code and other types of commercially proven practicability.

In practicing my invention, I attain the above and other objects and advantages by utilizing pulses of coded track circuit energy that have positive and negative polarities in alternating sequence and that are of relatively short individual duration. ergy preferably is supplied from positive and negative polarity sources that alternately are connected with the section rails by a continuously operating coding device. For imparting the desired shortness to the pulses I make use of a repeater relay which, with a brief delay, responds to each of the source-to-rrail connections that the coding device establishes. Upon each of those responses a contact of that relay interrupts the source-to-rail conn ction which produced the response and thereby causes all of the positive polarity pulses of trackway energy to be much shorter than the recurring code periods during which they occur and all of the negative polarity Such polar impulse code enpulses to be much shorter than the intervening code periods during which they occur.

I shall describe five forms of polar impulse coded track circuits which embody my invention, and shall then point out the novel features thereof in claims. These illustrative embodiments are disclosed by the accompanying drawings in which: 1 I

Fig. l is a diagrammatic representation of a single code track circuit that incorporates the improvements of my invention and that is of the detection only type;

Fig. 2 shows the Traclzway code for the circult of Pig. 1 and indicates the manner in which that code is produced and function which it performs; I

Fig. 3 illustrates a two-code track circuit that is equipped with the improved apparatus of my invention and that is organized to form part of a three indication system of automatic block signaling;

Fig. 4 shows a modified form of apparatus Which may be employed at the exit end of the Fig. 3 track section;

Fig. 5 illustrates apparatus suitable for repeating polar impulse code around the insu ated joints of a cut section; and

Fig. 6 shows the polar impulse rack circuit combination of Fig.3 supplemented by approach control facilities of novel non--line-wire type.

In the several views of the drawings, like reference characters designate corresponding parts. Referring first to Fig.1, characters I and 2 designate the conductors of a control circuit which normally is capable of transmitting energy between its two ends but which at times is rendered incapable of such transmission. As shown in Fig. 1, these control circuit conductors take the form of the two rails of a section of railway track II-III which isseparated from adjoining sections by the customary insulated'joints 3 and through which it will be assumed that traffic moves in the single direction indicated the arrow. Such movement, of course, makes location II the section entrance end and location III the section exit end.

Single-vote code combination of Fig.1

At this exit end III there is provided a source of positive polarity energy TP and. a so rce of negative polarity energy W; a coding device CT having a contact'ii which at any suitable speed (such as times per minute) repeatedly picks upand releases for the purpose of connecting in recurring code pulse manner the section rails first with the positive source TP and then with the negative source TN; and a repeater relay CP energized over a contact 6 of device CT and having a contact 1 which shortens the pulses of both positive and negative polarity that are impressed upon the section rails.

At the section entrance end 11 there likewise is provided a track relay TR of the code following type which has its winding connected across the rails and which holds contacts 8-9 to the left during each positive polarity pulse of windingreceived energy and to the right during each negative polarity pulse of received energy; a decoding transformer DT which receives primary current under the control of'the pole changing contact 8 of the track relay; and a code detect- 7 ing relay H which is of the direct current delayed release type and which is energized from the decoding transformer secondary over a rectifying contact 9 of the track relay.

The exit end or location III apparatus just described for the Fig. 1 track section operates in the following manner. Each pick-up or front closure of coding contact 5 produces a Positive period in the trackway ehergy code that is represented in Fig. 2. During the continuance of the energy pulse which defines that period,

. source TP maintains rail I positive with respect to rail 2. This is done over a connection extending from the positive terminal of source TP through front contact 5 of device CP, conductor II, a current limiting impedance I2, the track rails I and 2, conductor I3, and contact I of relay CP in its right or reverse position (shown dotted) back to the negative terminal of source TP.

Upon each release of the coding contact 5 there is produced a Negative period in the trackway code of Fig. 2. During the continuance of the energy pulse which defines that period, the negative source TN maintains rail I nega tive with respect to rail 2 (or rail 2 positive with respect to rail I). This is done over a connection extending from the positive terminal of source TN through contact I of relay CP in a left or normal position (shown in full lines), conductor I3, track rails 2 and I, impedance I2, conductor II, and the back contact 5 of device CT back to the negative terminal of source TN.

Device CT may take the form of a conventional code transmitter which repeatedly picks up and releases contacts 5'-& at some preselected rate such as 180 times per minute and in the usual code producing manner. The repeater relay CP therefor is of the magnetically toggled code following type and it has a delayed response of the short charatcer later described. When the left portion of its winding is energized over device CTs front contact 6, the relay holds its contact I in the left or normal position; when, however, the right portion of the relay winding is energized over CTs back contact 6, the relay holds contact I in the right or reverse position. Once, moreover, either of these positions is established, the contact I there remains continuously until the winding of relay 0? receives energy of the. opposing polarity.

In the exit end organization shown, therefore, each back contact closure of the coding device CT causes the repeater relay to shift its contact I from the left or normal to the right or reverse position and each front contact closure of device CT causes the relay to shift contact I from this right or reverse position back to the left or normal position. Accompanying each of these shifts is a short delay which will best be understood upon reference to Fig. 2.

In the diagram of that figure the elevated portions of the CTCR pattern designate picked-up conditions of contacts 5-45 while the depressed portions of the same pattern designate released conditions of those contacts. Similarly, the elevated portions of the CP pattern designate a normal or left closure of contact I while the depressed portions of the pattern designate a reverse or right closure of the same contact. From this Fig. 2 diagram it is apparent that due to relay CPs delayed responding characteristics: (l) a short interval elapses between each application of relay energy over front contact 6 and the opening of reverse contact I; and (2) a short interval elapses between the closure of back contact 6 and the movement of contact I from its normal to its reverse position.

Each of the rail supply circuits earlier traced is completed only for the duration of that short interval. In consequence the recurring pulses of positive polarity energy supplied from source TP are rendered much shorter than the recurring code periods which those pulses define, and the pulses of negative polarity energy from source TN likewise are rendered much shorter than the intervening code periods which those pulses define.

Examining Figs. 1 and 2 in greater detail, if contacts 55 of device CT reach their picked-up position at point a then the repeater relay contact I will begin movement from its reverse to its normal position at the slightly later point 1). Likewise, if the coding device contacts reach their released position at point c, then the repeater relay contact I will begin movement from its normal to its reverse position at the slightly later point d.

Each of the positive pulses of trackway energy supplied from source TP will therefore be of the relatively short duration designated at a b in Fig. 2 and each of the negative pulses supplied from trackway source TN will have a corresponding shortness designated by cd in Fig. 2. As compared with the total length a-c and c-e of the Positive and Negative code periods which the just named pulses respectively define, the

duration of energy application will be seen to be relatively short.

Looking next at the entrance end or location II apparatus earlier described for the Fig. 1 track section, it will first of all be observed that the track relay TR also is a code following device of the magnetically toggled polarized or polar stick type. During each pulse of positive polarity energy received from the section rails (rail I positive with respect to rail 2) the relay holds contacts 39 in the left or normal position; similarly, during each negative polarity energy pulse that is received by the relay winding contacts 8-9 are held in the right or reverse position.

A track relay of the represented polar stick I type is, moreover, capable of transferring its contacts from one position to the other rather rapidly and in response to only a short application of winding energy. This action is shown by the lower portion of Fig. 2. There the elevated portions of the TR pattern designate left or normal closures of the relay contacts while the depressed portions of the pattern designate right or reverse contact closures. Inasmuch as a shift from one position to the other takes place within the limits of the relatively short pulses of trackway energy represented above the pattern, the operation of the track relay is exactly the same as were each of the positive pulses to be prolonged for the full duration of the positive code period and each of the negative pulses to be prolonged for the full duration of the negative code period.

The code detector relay H is controlled by track relay TR in such manner that it holds its contact l8 picked up when and only when relay TB. is following code. Pick-up current is transmitted to the relay winding from control source terminals plus and minus and through decoding transformer DT. Contact 8 of relay TR serves to pole change the transformer exciting energy while contact 9 of the track relay mechanically rectifies the resulting transformer output in a manner which is disclosed and claimed by Frank H. Nicholson et al. Patent No. 2,237,788 issued April 8, 1941.

, As long as the track relay TR receives recurring pulses of positive and negative polarity trackway energy and shifts contacts 8-9 between their normal and reverse positions in step with those pulses, this code detector relay H receives the code frequency pulses of unidirectional current which hold contact I8 continuously picked up. In the event, however, that contacts 8-9 stay in one position continuously no secondary voltage is generated by transformer DT and relay H then is allowed to release contact H3.

The functioning of the complete polar impulse track circuit combination of Fig. 1 will become tions of the apparatus at exit location III and at entrance location II. Coding and repeater devices CT-CP operate continuously and cause exit sources TP-TN to supply the section rails with trackway energy having the polar impulse character represented in Fig. 2. Under vacant conditions of the section this energy is transmitted to entrance end track relay TR.

In responding that relay repeatedly shifts contacts 89 between their normal and reverse positions and thereby causes lay H to hold contact l8 continuously picked up. Such picked-up condition persists, quite obviously, as long as track section II--III remains vacant.

Entry of rails |-2 in code detecting reuously in the position to which they were last 1 energized and thereby deenergizes code detecting relay H. As a result of that deenergization contact It; now releases.

As the train passes out of section II-III transmission or" the coded polar impulse energy to entrance end relay TB is once more resumed, contacts 8-9 thereof again follow code, transformer D'I once more supplies energizing current to the winding of relay H and contact is of that relay again picks up.

Any suitable use of code detector relays contact it may, of course, be made and because of the diversit of such possible uses there has been no attempt to represent any particular one of them. Typically, however, they will be of the detection only variety wherein relay H performs the single function of distinguishing between vacant and occupied conditions of the associated track section. Such a function is, of

apparent from the foregoing descrippicked up, the signal course, required in many signaling system applications of commercially well-known character.

MuZti-rate code combination of Fig. 3

Referring to Fig. 3, I have there shown a polar impulse coded track circuit combination which is suitable for use in a three-indication system of automatic block signaling. Such a system includes the usual wayside signal S which guards the entrance of each of the system rack blocks in conventional manner.

Each of tthe two signals SII and SIII which is shown in Fig. 3 is of the Well-known color light type comprising three lamps G, Y and R which when selectively lighted respectively display the indications of clear, approach and stop.

Controlling each of these signals is a polar impulse track circuit combination which utilizes all of the elements earlier described for Fig. 1 plus: (1) facilities at exit location III for selecting between two distinctive rates of trackway pulse supply; and (2) facilities at entrance location II for distinguishing between these two code pulse rates and for selecting the indication of wayside signal $11 in accordance with such distinction.

The added exit end facilities take the form of a pair of code transmitters IBSCT and T5CT having contacts ME and 15 which respectively operate at the rates of 180 and times per minute; a coding device CR which repeats the operation of one or the other of the two transmitters and which carries contacts 5 and t that exactly duplicate the correspondingly designated elements of Fig. 1; and a code selecting relay H having a contact H which when picked up assigns the driving circuit of device CR to trans mitter contact Bali and which when released transfers the driving circuit to transmitter contact 75. This relay H is energized in the manner shown at location II and it constitutes the code detecting device for the advance section of which location III marks the entrance end.

The added code distinguishing facilities at entrance location II take the form of a decoding relay D which supplements the code detecting relay H and which receives pick-up current from to receive pick-up current only when the associated track relay 'IR follows code at the or high speed rate but not when that track relay follows code at the 75 or slow speed rate.

Serving to select the indication displayed by When both of those relays are shows clear as a result of lamp G being energized over front contacts Iii; when relay H is picked up at a time that relay D is released the signal shows ap as a result of lamp Y being energized over front contact 3 and back contact ii); and

when relay H is released the signal shows stop as a result of lamp R receiving lighting current over back contact l8.

From the foregoing description of the polar impulse coded track circuit apparatus of Fig. 3 it will be apparent that by equipping each of a plurality of consecutive track sections with this Fig. 3 apparatus (and arranging that the entrance end relay H of each section determines,-

by means of contact ll as shown at location 111,- the rate of pulse recurrence of the polarized trackway energy that is supplied to the exit end of the rear adjoining section) there may be provided a three-indication automatic block signaling system of novel and improved character. Such a three-indication system will operate in the following manner.

As long as the signaled stretch of track remains vacant the rails of each section therein transmit to their entrance ends trackway energy pulses which are of the polar impulse character shown in Fig. 2 and which recur at the high speed code rate of 180 cycles per minute; the track relay TR for each section responds to those polarized pulses by cyclically shifting the position of its contacts 8-43 180 times per minute; the entrance end detecting and code distinguishing relays H and D for each section are thereby both held picked up; and the guarding signal S for each section is kept (by relays I-l-D) at clear.

In the event that a train now passes through the signaled stretch the rail shunting action of its wheels and axles produces the following effeet at the entrance end of each of the sections occupied: (l) de-energization of track relay TR; (2) release of decoding relays H and D; (3) placement at stop of the section guarding signa1 S; and (4) supply of slow speed or 75 cycle per minute polar impulse code energy to the section immediately to the rear.

At the entrance end of that first rear section the pulses of that 75 code energy: (1) cause the contacts of track relay TR to operate at the '75 code rate; (2) cause code detecting relay H to pick up; (3) put the signal S for that first rear section at approach; and (4) cause high speed or 180 polar impulse code energy to be supplied to the next section to the rear.

At the entrance of that next or second rear section the pulses of that 180 code energy: (1) operate the contacts of track relay TR at the 180 code rate; (2) hold decoding relays Hand D both picked up; (3) put the signal S for that second rear section at clear; and (4) cause 180 polar impulse code energy to be repeated into the rails of the succeeding section to the rear.

In this way each train passing through the signaled (as per Fig. 3) stretch of track sets up its own following protection in customary threeindication automatic block manner.

Referring to Fig. 4, I have there shown modifled exit end facilities for the track circuit combination of Fig. 3. These modified facilities eliminate the transmitter repeater device CR of Fig. 3 and substitute therefor a direct inclusion of contacts of the two code transmitters I8DCT and lECT in the energizing circuit for repeater relay CP and in the rail supply circuit for positive and negative trackway sources TP and TN.

In this Fig. 4 arrangement, transmitter contacts I80 and l5 perform the function of contact 6 of Fig. 3s contact device CR. By contact ll of code selector relay H one or the other of these transmitter contacts is included in the driving circuit for repeater relay CP. When relay H is picked up contact I80 of transmitter IBUCT is so included and when relay H is released contact of code transmitter l5CT is so included.

For performing the function of contact 5 of Fig. Ss coding device CR, the two transmitters IBGCT and l5CT are equipped with additional contacts lfifia and 15a. Selection between these contacts is effected by an added contact Ila of the code selector relay H. When picked up that contact Ila causes code transmitter contact l8lla to be included in the circuits over which sources TP and TN supply positive and negative energy pulses to the track section extending rearwardly from location III; when released contact Ila causes code transmitter contact 150. to be included in those rail supplying circuits.

The operation of the Fig. 4 exit end facilities will have become apparent from the foregoing description of the apparatus organization. With code selector relay H picked up, the high speed transmitter contacts I and 186a respectively drive repeater relay CP and determine the connection of positive and negative energy sources TP and TN with the section rails. Similarly, when relay H is released, low speed transmitter contacts l5 and 15a perform corresponding functions.

Without altering the complete system operation in any way the exit end facilities of Fig. 4 may, therefore, be substituted for those shown in Fig. 3 and the same automatic block protection as was earlier described for Fig. 3 will be effected by the so modified combination.

Cut-section facilties of Fig. 5

In certain instances it may be desirable to subdivide the main signal block II-III of the Fig. 3 system into two or more track sections. Typically, such subdivisions will be occasioned by requirements of excessive block length, highway crossing control or other equally well-known reasons. In the event of such subdivision, means must be provided for repeating into the rails of each rear section the coded energy that is supplied to the rails of each forward section.

Facilities for performing such code repeating functions are illustrated in Fig. 5. There a block subdividing or cut-section location 11a is shown as being occasioned by insulated joints 3 which are interposed between the entrance and exit locations of a signal block having the character represented at II-III in Fig. 3. Operated by the polar impulse code energy that is received from the forward section rails is a code following track relay TR having response characteristics that duplicate those of the correspondingly desig nated device in each of the Fig. 3 and Fig. 1 track circuit combinations.

Carried by this relay TR. are contacts 5 and 6 which perform exactly the same function as do elements 5 and 8 of device GB of Fig. 3 and of device DT of Fig. 1. That is, contact 5 determines the connection of positive and negative polarity energy sources TP and TN with the rails of the rearwardly extending section while contact 6 supplies operating energy to the winding of a repeater relay CP.

That repeater relay duplicates the correspondingly identified device of each of the Figs. 3 and l combinations and it carries a contact I which is included in the rear section rail supply circuit in exactly the same manner as in the earlier described organization of Figs. 1 and 3. The rear section energy sources TP and TN likewise have an exact correspondence to the similarly identifiedelements of the earlier figures.

In operation of the complete cut-section combination of Fig. 5, forward section track relay TR positions its contacts 5-'ri to the left upon each reception from the forward section rails of a positive polarity energy pulse and to the right upon each reception from the same rails of a negative polarity energy pulse. During the early portion of each of those left or normal contact positionings contact connects the rear section rails with the negative energy source TN and during the early portion of each of the right or reverse positionings contact 5 connects the rear section rails with the positive energy source TP.

Under the action of contact 7 of repeater relay CP each of the just named connections is, however, interrupted very early in the code period which the connection defines, and in consequence the alternate positive and negative energy pulses which are repeated into the rear section rails have the same impulse character as is represented in Fig. 2. That is, each positive pulse is short as compared with the total code period length which the pulse defines and each negative pulse also persists only during a small portion of the defined negative code period.

The particular cut-section combination of Fig. 5 is, as will be noted, of the inverse polarity repeating character. That is, each positive pulse received from the forward section rails causes a negative pulse to be repeated into the rear section rails and each pulse of negative forward section energy causes a pulse of positive energy to be supplied to the rear section. Alternatively, of course, sources TP and TN might be interchanged and in that event a direct polarity coincidence would result between the received pulses of forward section energy and the repeated pulses of rear section energy. With either arrangement, quite obviously, the basic form of track and relay operation is the same.

Approach control organization of Fig. 6

the automatic block signaling applications of Figs. 1 and 3, these track circuits may also be organized into non-line-wire approach control combinations of the character represented in Fig. 6.

By that figure the basic track circuit combination of Fig. 3 is reproduced and two supplemental relays KR and AR also are shown..

These relays serve to keep the associated wayside signal SIII deenergized at all times except when a train approaches the signal location over the rails of section 11-111, and they do this through the medium of a contact 2| carried by relay AR.

Relay KR will be referred to as a detector device. It is of the magnetically biased polar responsive code following type and the winding thereof is bridged across the section rails through the medium of an impedance 22. The illustrated connection is of the well-known floating type wherein the relay is energized by the voltage complement of the coded energy pulses that are supplied to the section rails.

Each connection of the positive polarity source 'I'P with the rails thus causes relay KR to receive potential which makes it left terminal positive with respect to the right and each connection with the rails of the negative polarity source TN similarly causes relay KR to receive potential which makes the right terminal of its Winding positive with respect to the left terminal. In other words, trackway energy having the polar impulse character shown in Fig. 2 is impressed upon the winding of relay KR under all vacant conditions of track section II-III.

Each positive pulse of this energy positions contacts 23 and 24 of relay KR to the left while each negative polarity pulse of the applied energy moves those contacts to the right or reverse position. Once in either position the contacts will stay until the relay winding is energized in a direction to move them to the opposite position.

Controlled by contacts 23 and 24 through the medium of an interposed transformer AT is the companion or approach relay AR. This relay is of the direct current type and its contact 2| is sufficiently slow in releasing to bridge the intervals between recurrent movements of contacts 23-24 during code following operation of the detector relay KR.

Pick-up current for relay AR is transmitted thereto during and only during code following operation of the detector relay contacts 2324. Together with transformer AT these contacts are interposed between relay ARs energizing source terminals plus and minus in such manner as to constitute a mechanical rectification combination of the character earlier identified with Nicholson et al. Patent 2,237,788.

In operation of the approach control facilities of Fig. 6, the continuously operating coding and repeater devices CR-CP alternately'connect the track rails l and 2 with the positive and negative polarity sources TP and TN over a circuit which includes the current limiting impedance 12. As long as the track section to the rear of location III remains vacant the then supplied pulses of positive and negative potential appearing between rails I and 2 are substantially or the full terminal voltages of sources TP and TN.

Those voltages are sufiiciently high to cause the detector relay KR to move contacts 23-44 to their left or normal positions upon the occasion of each positive polarity pulse and to their right or reverse positions upon the occasion of each negative polarity pulse. In consequence of the resulting code following action of contacts 23-24, the transformer AT transmits to the approach relay AR recurring pulses of unidirectional current which hold contact 2| of that relay continuously picked up. Such pick-up maintains the lighting circuits of the wayside signal SIII disconnected from their energizing source and thereby continues the signal inactive as long as the track section in the rear of location III remains vacant.

In the event now that a train comes into the section, the usual shunting action of its wheels and axles reduces the potential appearing between rails l and 2 at the section exit and causes much of the voltage of each of the rail connected sources TP and TN to appear in the form of a potential drop through impedance l2. This reduction in exit end rail potential progressively increases as the train approaches location III and eventually becomes so great that the detector relay KR is no longer able to respond to the positive and negative polarity pulses which sources TP and TN alternately supply.

Upon such advancement of the approaching train relay KR accordingly ceases to shift the position of contacts 23-24 and instead allows those contacts to remain in the position to which they were last energized. As a result, transformer AT now discontinues all transmission of pick-up energy to relay AR and causes that relay to release contact 2 I. That release, of course, connects the wayside signal $111 with its lighting source and thereby causes that signal to display the particular indication which is selected by decoding equipment H-D.

again picks up contact 2i and thereby restores the wayside signal SIII to its normally inactive condition.

While the improved approach control facilities of Fig. 6 have been explained in an application wherein the lights of wayside signals only are approach governed, it will be understood that these facilities have equal utility when used with approach control combinations which provide for other comparable functions instead of or in addition to the illustrative one here illustrated.

Summary From the foregoing it will be seen that the improved polar impulse coded track circuits of my invention are of broad utility and that their application is by no means restricted to the detector only, the automatic block signaling, and the approach control forms which are herein shown by way of illustration.

Such polar impulse track circuits offer a number of important advantages to which attention will now be directed. First, they cut down power requirements. Since the periods of rail energy application are very brief (see Fig. 2) much less power is required from the trackway sources I? and TN than is the case with conventional coded organizations wherein each energy pulse continues for the full duration of the code period which the pulse defines.

Second, my improved track circuits offer foreign current protection of a superior character. The utilized track relay TR, (and KR of Fig. 6) can be operated only by trackway energy which is of periodically reversed polarity (again see Fig. 2). Unless foreign current reaching the relay is of that special character it quite obviously cannot produce false operation.

Third, my improved polar impulse traclr circuits eliminate storage effect difficulties to a greater extent than has been possible in the past. Energy stored in the track ballast and rails following each application of code pulse energy thereto retains the polarity of the applied pulse and the potential thereof can progressively build up only when successive applied pulses are of the same polarity. By my alternate reversals of applied pulse polarity (once more see Fig. 2) I keep the level of storage potential far below that which is effective to produce false track relay operation.

Fourth, my improved track circuits minimize code distortion difficulties. Such difficulties are largely due to storage energy and when it is reduced to the extent just stated they practically disappear. Moreover, the utilized track relays TR (and KR of Fig. 6) are of the magnetically toggled type and, as indicated by Fig. 2, each requires only a very short pulse of polarized energy to shift its contacts. Such a pulse represents only a very small portion of the total defined code period and thus permits a relatively wide variation in code pulse spacing without interfering with the desired pulse responsive operation of the track relay. To be noticeable,

- therefore, distortion effects must be far more e'xtreme than are ordinarily encountered.

Fifth, my new track circuits readily lend themselves to improvements in shunting sensitivity characteristics. Such improvements may be effected by raising the voltage of the applied trackway energy. Due to the relative shortness of the applied polar impulse pulses, voltage elevations of my trackway sources do not increase the total power consumption to an objectionable extent.

Sixth, the polar impulse principle permits operation of longer track circuits on less voltage. Track relays of the polar stick type herein illustrated can be designed to respond to less power than can code following track relays of the conventional polar biased type and they are, therefore, operable on track circuits of extended length.

From the foregoing description of Figs. 1 to 6, inclusive, it will be seen that in addition to improving the performance and other characteristics of coded track circuits per se, I have also made important improvements in complete railway signaling systems of the coded track circuit class. In particular, I have lowered the power requirements of such systems; I have rendered the systems track relays highly immune to false operation by foreign current that may be present in the track rails; I have eliminated operating difficulties due to persistance of storage energy in the track ballast and rails following each pulse of coded energy that is applied thereto; I have minimized the effects of code distortion on the operation of track circuits of the coded type; I have improved the shunting sensitivity of such circuits and have extended the length over which they may be operated with a given level of applied energy; I have provided improved facilities for impressing the coded energy upon the track rails and for imparting a highly effective character to the pulses of that energy; and I have organized the improved facilities in such manner that the resulting track circuits are readily usable in signaling systems of the frequency code and other types of commercially proven practicability.

Although I have herein shown and described only a few forms of coded track circuits embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a control circuit that includes a pair of conductors which normally are capable of transmitting energy between given and opposite ends of the circuit but which at times are rendered incapable of such transmission, a source of positive polarity energy and a source of negative polarity energy at the given end of said circuit, a coding device which repeatedly connects said circuit conductors first to said positive polarity source and then to said negative polarity source and thereby produces a control code made up of recurring pulses of positive polarity energy which are separated by intervening pulses of negative polarity energy, a repeater relay for said coding device which with a brief delay responds to each of the said conductor-to-source connections that said device establishes, a contact of said repeater relay which interrupts each of said conductor-to-source connections early in the code period that the connection defines and which thereby causes all of said positive polarity pulses to be much shorter than the recurring code periods during which they occur and all of said negative polarity pulses to be much shorter than the intervening code periods during which they occur, a code following relay connected with said conductors at the opposite end of said circuit and operated by the said shortened pulses of polarized control code energy that are there received, and apparatus controlled by said code following relay and distinctively responsive according as that relay is or is not following code.

2. In combination, a control circuit that includes a pair of conductors, a source of positive polarity energy and a source of negative polarity energy at one end of said circuit, a similarly located coding device having a first contact which repeatedly connects said circuit conductors first to said positive polarity source and then to said negative polarity source and which thereby produces a trackway code made up of recurring pulses of positive polarity energy that are separated by intervening pulses of negative polarity energy, a second contact of said coding device which operates in synchronous relation with respect to said first contact, a repeater relay for said coding device which is energized over said second contact and which responds after a brief delay to each of the said conductor-to-source connections that said first contact establishes, a contact of said repeater relay which interrupts each of said conductor-to-source connections early in the code period that the connection defines and which thereby causes all of said positive polarity pulses to be much shorter than the recurring code periods during which they occur and all of said negative polarity pulses to be much shorter than the intervening code periods during which they occur, a code following relay connected with said circuit conductors and operated by the said shortened pulses of polarized control code energy that are received therefrom, and apparatus controlled by said code following relay.

3. In combination, a control circuit that includes a pair of conductors, a source of positive polarity energy and a source of negative polarity energy for said circuit, a coding device having a contact which shifts from a front position to a back position and from said back to said front position in regularly recurring manner, a repeater relay governed by said coding device anl having a contact which upon each back contact closure of that device moves after a brief delay from a normal to a reverse position and which upon each front contact closure of the coding device moves after a brief delay from said reverse to said normal position, a connection which is completed over the front point of said coding device contact and the reverse point of said repeater relay contact and through which said positive polarity source supplies said circuit conductors with recurring pulses of positive polarity energy that are much shorter than the control code periods which those pulses define, another connection which is completed over the back point of said coding device contact and the normal point of said repeater relay contact and through which said negative polarity source supplies said circuit conductors with intervening pulses of negative polarity energy that are much shorter than the control code periods which those pulses define, a code following relay connected with said circuit conductors and operated by the said shortened pulses of polarized control code energy that are received therefrom, and app Cont-rolled by said code following relay.

4. In combination, a section of railway track, a source of positive polarity energy and a source of negative polarity energy for the rails of said section, a coding device which repeatedly connects said rails first to said positive polarity source and then to said negative polarity source and thereby produces a trackway code made up of recurring pulses of positive polarity energy that are separated by intervening pulses of negative polarity energy, a repeater relay for said coding device which with a brief delay responds to each of the said rail-to-source connections that said device establishes, a contact of said repeater relay which interrupts each of said railto-source connections early in the code period that the connection defines and which thereby causes all of said positive polarity pulses to be much shorter than the recurring code periods during which they occur and all of said negative polarity pulses to be much shorter than the intervening code periods during which they occur, a code following track relay operated by the said shortened pulses of polarized trackway energy that are received from said rails, and apparatus controlled by said track relay.

5. In combination, a section of railway track, a source of positive polarity energy and a source of negative polarity energy at one end of said section, a coding device which repeatedly connects the section rails first to said positive polarity source and then to said negative polarity source and thereby produces a trackway code made up of recurring pulses of positive polarity energy which are separated by intervening pulses of negative polarity energy, a repeater relay for said coding device which with a brief delay responds to each of the said rail-to-source connections that said device establishes, a contact of said repeater relay which upon each of said responses interrupts the said rail-to-source connection that produced the response and which thereby causes each of said trackway energy pulses to be much shorter than the period of said trackway code that the pulse defines, a magnetically toggled code following track relay connected with said rails and operated by the said shortened pulses of polarized trackway energy that are received therefrom, and apparatus controlled by said track relay and distinctively responsive according as that relay is or is not following code.

6. In combination, a section of railway track, a source of positive polarity energy and a source of negative polarity energy for the rails of said section, a continuously operating coding device having first and second which said first contact repeatedly connects the section rails first to said positive polarity source and then to said negative polarity source and thereby produces a trackway code made up of recurring pulses of positive polarity energy which are separated by intervening pulses of negative polarity energy, a repeater relay energized over said second contact of the coding device and responding with a brief delay to each of the said rail-to-source connections that said first coding device contact establishes, a contact of said repeater relay which upon each of said responses interrupts the said rail-to-source connection that immediately preceded the response and which thereby causes each of said trackway energy pulses to be much shorter than the period of said trackway code that the pulse defines, a code following track relay operated by the said shortened pulses of polarized trackway energy that are received from said rails, and apparatus controlled by said track relay.

7. In combination, a section of railway track, a source of positive polarity energy and a source of negative polarity energy for the rails of said section, a coding device having a contact which shifts from a front position to a back position and from said back to said front position in regularly recurring manner, a repeater relay governed by said coding device and having a contact which upon each back contact closure of that device moves after a brief delay from a normal to a reverse position and which upon each front contact closure of the coding device moves after a brief delay from said reverse to said normal position, a circuit which is completed over the front point of said coding device contacts and the reverse point of said repeater relay contact and through which said rails are by said positive polarity source supplied with recurring pulses of positive polarity energy that are much shorter than the trackway code periods which those pulses define, another circuit which is completed over the back point of said coding device contact and the normal point of said repeater relay contact and through which said rails are by said negative polarity source supplied with intervening pulses of negative polarity energy that are much shorter than the trackway code periods which those pulses define, a code following track relay operated by the said shortened pulses of polarized trackway energy that are received from said rails, and apparatus controlled by said track relay.

8. In combination, a stretch of railway track, a track section included in said. stretch, a source of positive polarity energy and a source of negative polarity energy at the exit end of said section, first and second coding contacts which respectively operate at high speed and low speed rates, means governed by one or the other of said contacts for repeatedly connecting the rails of said section first to said positive source and then to said negative source whereby way code made up of recurring pulses of positive polarity energy that are separated by intervening pulses of negative polarity ener y, means governed by traffic conditions in advance of said section for selecting between said first and second coding contacts whereby to cause sa1d polarized pulses of traclzway energy to recur at said high speed rate at times and at said low speed rate at other times, a repeater relay for said selected coding contact which interrupts each of said contact-governed. rail-to-source connections early in the code period that the connection defines and which thereby causes all of said polarized energy pulses to be much shorter than the trackway code periods during which they occur, a code following track relay located at the entrance end of said section and operated by the said polarized energy pulses that are there received from the section rails, and trafiic governing apparatus controlled by said track relay and responding distinctively to each code pulse rate at which that relay operates.

9. In combination, a stretch of railway track, a track section included in said stretch, a source of positive polarity ener y and a source of negative polarity energy at the exit end of said section, first and second code transmitter contacts respectively operating at high speed and low speed rates, a coding device which repeats the operation of one or the other of said two .code

to produce a tracktive polarity energy for transmitter contacts, means governed by traffic conditions in advance of said section for selecting between those contacts whereby to cause said coding device to operate at said high speed rate at times and at said low speed rate at other times, a contact of said so operated coding device which repeatedly connects the rails of said section first to said positive source and then to said negative source and thereby produces a traclzway code made up of recurring pulses of positive polarity energy that are separated by intervening pulses of negative polarity energy, a repeater relay for said coding device which interrupts each of said rail-to-source connections early in the code period that the connection defines and which thereby causes all of said polarized energy pulses to be much shorter than the trackway code periods dur ing which they occur, a code following track relay located at the entrance end of said section and operated by the said polarized energy pulses that are there received from the section rails, and. traf'fic governing apparatus controlled by said track relay and responding distinctively to each code pulse rate at which that relay operates.

10. In combination, adjoining forward and rear sections of railway track, means for supplying the rails of said forward section with coded energy in recurring pulse form, a code following track relay for said forwardsection operated by said coded energy and having a contact which during such operation shifts from a first position to a second position and from said second to said first position in regularly recurring manner, a source of positive polarity energy and a source of negathe rails of said rear section, circuits over which said track relay contact connects said rear section rails to said positive source when in said first position and to said negative source when in said second position and thereby produces a trackway code made up of recurring pulses of positive polarity energy which are separated by intervening pulses of negative polarity energy, a repeater relay governed by said track relay and responding with a brief delay to each of the said rail-to-source connections that said track relay contact establishes, and a contact of said repeater relay which upon each of said responses interrupts the said rail-to-source connection that immediately preceded the response and which thereby causes each of said trackway energy pulses to be much shorter than the period of said trackway code that the pulse defines.

ll. In combination, adjoining forward and rear sections of railway track, means for supplying the rails of said forward section with coded energy in the form of recurring pulses having positive and negative polarities in alternating sequence, a code following track relay for said forward section operated by said polarized pulses of coded energy and having a contact which during such operation shifts from a normal position to a reverse position and from said reverse to said normal position in regularly recurring manner, a repeater relay governed by track relay and having a contact which upon each of that relays reverse contact closures moves after a brief delay from a normal to a reverse position and which upon each of the track relays normal contact closures moves after a brief delay from said reverse to said normal position, a source of positive polarity energy and a source of negative polarity energy for the rails of said rear section, a connection which is completed over the normal point of said track relay contact and the reverse point of said repeater relay contact and through which said positive polarity source supplies said rear section rails with recurring pulses of positive polarity energy that are much shorter than the track- Way code periods which those pulses define, and

another connection which is completed over the I reverse point of said track relay contact and the normal point of said repeater relay contact and through which said negative polarity source supplies said rear section rails with intervening pulses of negative polarity energy that are much shorter than the trackway code periods which those pulses define.

12. In combination, a section of railway track, a source of positive polarity energy and a source of negative polarity energy at the exit end of said section, a coding device which repeatedly connects the section rails first to said positive source and then to said negative source and thereby produces a trackway code made up of recurring pulses of positive polarity energy that are separated by intervening pulses of negative polarity energy, a code following detector relay installed at said section exit, an operating winding for said detector relay connected to receive a component of the said positive and negative pulses of coded energy that are present in said section rails, a contact of said detector relay which shifts between normal and reverse positions in step with the said positive and negative polarizations of that energy when and only when said winding received component thereof has the relatively high value which accompanies a predetermined trafiic condition of said section, a slow release approach relay which is held picked up by current received over said detector relay contact during said code following shifts thereof but which releases whenever that contact fails to follow code, and traific governing apparatus having an energizing circuit controlled by said approach relay and completed when and only when that relay occupies a preselected one of its positions.

13. In combination, a section of railway track, a source of positive polarity energy and a source of negative polarity energy at the exit end of said section, a coding device which repeatedly connects the section rails first to said positive source and then to said negative source and thereby produces a trackway code made up of recurring pulses of positive polarity energy that are separated by intervening pulses of negative polarity energy, a repeater relay governed by said coding device and responding with a brief delay to each of the said rail-to-source connections that said device establishes, a contact of said repeater relay which upon each of said responses interrupts the said rail-to-source connection that immediately preceded the response and which thereby causes each of said trackwav energy pulses to be much shorter than the period of said trackway code that the pulse defines, a code following detector relay installed at said section exit, an operating winding for said detector relay connected to receive a component of the said shortened pulses of polarized coded energy that are present in said section rails, a contact of said detector relay which shifts be tween normal and reverse positions in step with the said positive and negative polarizations of that energy when and only when said winding received component thereof has the relatively high value which accompanies a predetermined trafiic condition of said section, a slow release approach relay which is held picked up by current received over said detector relay contact during said code following shifts thereof but which releases whenever that contact fails to follow code, and trairlc governing apparatus having an energizing circuit controlled by said approach relay and completed when and only when that relay occupies a preselected one of its positions.

14. In combination, a section of railway track, a source of positive polarity energy and a source of negative polarity energy at the exit end of said section, a coding device which repeatedly connects the section rails first to said positive source and then to said negative source and thereby produces a trackway code made up of recurring pulses of positive polarity energy that are separated by intervening pulses of negative polarity energy, a code following detector relay at said section exit having an operating winding bridged across said section rails and being provided with a contact which shifts between normal and reverse positions in step with the said positive and negative polarizations of said rail energy under all vacant conditions of said section and also until a rail-shunting train approaches said section exit closely enough to decrease the potential of the there supplied rail energy to a value too low to operate the detector relay, a slow release approach relay which is held picked up by current received over said detector relay contact during said code following shifts thereof but which releases whenever that contact ceases to follow code, and trafiic governing apparatus having an energizing circuit controlled by said approach relay and completed when and only when that relay is released.

HOWARD A. THOMPSON. 

